Color picture tube grid structure with nonuniform generally parallel slits

ABSTRACT

A grid structure for color picture tubes adapted to decrease undesirable deviation of electrons away from the phosphor screen of a color picture tube. The slits between the grid wires are formed narrower at the upper and lower portions and wider in the central portion to increase the fundamental vibration frequency and increase the electron beam transmission factor. The latter grid structure eliminates the deleterious effects of (a) grid vibration caused by accidental impact and (b) earth magnetism.

United States Patent [72] Inventor Makoto Maeda Kanagawa-ken, Japan [21 Appl. No. 798,635

[22] Filed Feb. 12, 1969 [45] Patented Apr. 6, 1971 [73] Assignee Sony Corporation Tokyo, Japan [32] Priority Feb. 12, 1968 [33] Japan [54] COLOR PICTURE TUBE GRID STRUCTURE WITH NONUNIFORM GENERALLY PARALLEL SLITS Primary Examiner-Robert Segal AttorneysAlbert C. Johnston, Robert E. Isner, Lewis H.

Eslinger and Alvin Sinderbrand ABSTRACT: A grid structure for color picture tubes adapted to decrease undesirable deviation of electrons away from the 1 Claim 4 Drawing Figs phosphor screen of a color picture tube. The slits between the [52] US. Cl 313/85, grid wires are formed narrower at the upper and lower por- 313/349, 313/86 tions and wider in the central portion to increase the funda- [51] lnt.Cl ..H01j 29/06, mental vibration frequency and increase the electron beam HOlj 29/46,H0lj 29/56 transmission factor. The latter grid structure eliminates the [50] Field of Search 313/87, 92 deleterious effects of (a) grid vibration caused by accidental (PDF), 85 impact and (b) earth magnetism.

i i 7 "1 a a a J J J n H l P i H n J J Li D u F i lL T a /.4 f4 ,2 /3 14 Patented April 6, 1971 2 Sheet s-Sheet 1 FIG. 4

80,41 I a/a 8% 5w, M44 1 z INVENTOR. MAKOT'O MAEDA BY Q 4 ATTORNEY ill tCULOR WCTURE TUBE GRID STRUCTURE Wl'llllll NONlUNWORM GENERALLY PARALLEL SLLTS BACKGROUND OF THE INVENTION Color cathode ray tubes employ, for electron beam post deflection and focusing, a grid structure in which a plurality of grid wires are stretched across a frame which is generally in the form of a parallelogram. These grid structures are produced by stretching a plurality of parallel grid wires across opposed portions on a master frame under a predetermined amount of tension. A grid frame is then put on the grid wires from inside the master frame and then the grid wires are fixed to a pair of opposed supports on the grid frame, thereafter being severed along the margins of the grid frame. In this case, the grid frame is prestressed inwardly by a tumbuckle to apply maximum tension to the grid wires secured to the central portion of the opposed supports of the grid frame and a lesser amount of tension to those wires fixed to the end portions of the supports, insuring that all the grid wires are subjected to substantially uniform tension by the restoring force of the prestressed grid frame after disassembling it from the master frame.

Such a grid structure may be regarded as one in which a plurality of grid wires are stretched at substantially uniform tcnsion on a frame which is prestressed in a manner to be displaced the most at the central portion of the frame. When a predetermined positive potential is applied to such grid structure and electron beams are emitted from the electron gun of a cathode ray tube toward the fluorescent screen thereof, electron beams of several to l-odd percent strike the grid wires and are discharged therethrough to thereby heat the grid wires. As a result of this, the temperature of the grid wires is raised sufficiently to cause the wires to expand. An examina tion of the expanded grid wires shows that since the displacement of the frame is greatest at the center portion, elongation of the grid wires of that portion due to the thermal expansion is cancelled by the restoring force of the prestressed frame as if the grid wires have not been elongated. Accordingly, the grid wires are still subjected to substantially the same tension as the predetermined amount, and hence do not sag. The elongation of the grid wires lying on both sides of the central grid wires clue to thermal expansion cannot be absorbed with the displacement of the frame at those particular portions, since the displacement is basically small. Consequently, when the elongation of the grid wires exceeds the displacement of the frame, the grid wires are likely to sag. Even if the grid wires do not sag, they are not pulled at a predetermined tension and are readily vibrated at great amplitude to lower the picture quality of the reproduced picture when subjected to accidental small shocks.

The above can easily be understood from the fact that when all the grid wires have substantially the same length ll, their elongation resulting from thermal expansion is Al and the amount of restoration of the distorted frame is All at the center thereof; the amount of restoration of the frame on both sides of the center thereof is smaller than that at the central portion.

SUMMARY OF THE INVENTION This invention seeks to overcome the drawbacks of the prior art by constructing the grid elements and the spacing therebetween in such a manner that the electron beam transmission factor is greatest at the central portion of the grid structure. Thus, the individual grid elements are relatively narrow at the intermediate portion of their length and are wider at their end portions thereof. The spacing between the grid elements is widest at the intermediate portion of the slit forming the space and narrowest at the end portions thereof.

It has been determined that the aforementioned construction of the grid elements and spacing therebetween will suppress the deleterious effects of magnetic forces and also contributes to suppress the mechanical resonance of the grid elements.

Therefore, it is an object of this invention to provide a grid structure having grid elements of a predetermined configuration to eliminate electron beam deviation.

Another object of the invention is to provide a color picture tube which is virtually free of the deleterious effects of magnetism.

A further object of the invention is to provide a color picture tube which utilizes a grid structure having a high resistance to vibration caused by an external force.

An additional object of the invention is to provide a color picture tube in which the electron beam transmission factor is high at the central portion of the grid to provide increased luminance.

BRlEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of a grid plate;

FIG. 2 is a cross-sectional view showing the manner in which grid elements are mounted on a grid frame;

H6. 3 is a plan view, partly cut away, showing details of the grid plate; and

F l0. 4 is a schematic diagram showing the width of slits formed in the grid plate.

DESCRlPTlON OF THE PREFERRED EMBODlMlENT Referring to FIG. ll, there is shown a grid plate 10 which can be made by photoetching or the like to remove selected areas of a sheet metal plate ill of stainless steel, for example. The grid plate ill can be a parallelogram such as a rectangle, square or any other desired shape and can be manufactured using any known process.

Grid elements 113 are arranged parallel to each other across the face of the plate Ill and are arranged at a predetermined desired pitch. Peripherally arranged along the edges bordering the upper and lower ends of the grid elements respectively are slits M. Each slit 14 corresponds to a plurality of grid elements 113 (three in the illustrated example). A slot 15 is provided on opposed ends of the plate 111 which is parallel to the grid elements 13. The slits M serve to separate a series of tabs 16.

The grid frame may take the form of a pair of bars 118 as disclosed in the aforementioned copending US. Pat. application. The tabs 116 separated by the slits M are respectively held by opposed chucks 19 such that each tab is held by a chuck. Either one set or both sets of chucks are placed under moderate tension in accordance with the length and the quality of the tab material so as to obtain a predetermined distribution of tension which will be ultimately applied to the grid elements 113. In FIG. 2 each chuck is placed under tension by means of a coiled spring 20. The chucks 19 are disposed in accordance with the configuration of the grid frame, so that the grid plate W is maintained taut and the plate conforms to the shape of the grid frame. While the grid plate is held taut, the grid plate is welded to a pair of bar supports llfl which are placed in a predetermined position on the grid plate.

Subsequent to the welding of the grid plate to the bar supports llfl, the tabs 116 which have a portion projecting beyond the bar supports 118 are cut off. The slot which facilitates the cutting of the plate 10 can also be cut off. In this manner, the grid elements 13 can readily be mounted on the bar supports 11% of the frame under a predetermined distribution of tension.

By utilizing the above arrangement, the slits 11d prevent the grid plate 110 from bending or buckling when applying a predetermined tension to the tabs 16.

Grid structures which are manufactured by the aforementioned process do not fully insure that the electron beam will impinge on the color tube because of the influence of the earth's magnetism. This is especially true at the upper and lower portions of the grid structure. Also, when the grid structure is subjected to an external force such as mechanical vibration or the like, the grid elements will oscillate, which also causes deviation of the electron beam at the central portion of the grid structure.

ln order to obviate the influence of the earths magnetism, it is possible to narrow the width of the elongated slits 17 by enlarging the adjacent grid element 13 as shown in FIG. 1. The disadvantage in this, however, is that the luminance of the reproduced picture appreciably lowers and the wider grid element has a lower mechanical resonant frequency resulting in an increased deviation of the electron beam because of increased vibration of the grid elements. To overcome these disadvantages, I have constructed the slits 17 so as to be wide at the central portion thereof and to gradually decrease in width toward the edges of the plate 10. The shape of the slit 17 being somewhat like a spindle as clearly shown in FIG. 3, the adjacent grid elements 13 are exactly the opposite, that'is, the grid element is narrow at the central portion of its length and it gradually increases in size as one approaches theopposite edges of the plate 10.

With this construction, the slits 17 are narrower at the upper and lower end portions than at the central portion, so that deviation of the electron beam is not caused even under the influence of the horizontal component of the earth's magnetism. The central portion of each slit 17 is relatively larger in width than the opposed ends, and accordingly the electron beam transmission factor at the central portion is highJThis, of course, appreciably increases the luminance at the central portion of the reproduced picture produced by a color picture tube equipped with the grid structure of this type. When' the luminance is increased at the central portion of the reproduced picture, the viewer has a feeling that the luminance of the entire screen area of the reproduced picture has been increased from the nature of vision. The viewer thereby obtains an impression similar to that given by a bright and vivid reproduced picture. I

The formation of the spindle-shaped slits 17 makes the grid elements 13 narrow at the central portion. When an external force, such as vibration, has been rendered to the grid structure, the resonant frequency of each grid element is raised which insures an appreciable decrease in electron beam deviation. This can be demonstrated mathematically by the following: let it be assumed that grid elements of a length L are stretched along an X-axis and are secured at positions x==o and FL, and the line density of the grid elements is taken as p.(X). The movement of the grid elements in a direction perpendicular to the X-axis is given by the following equation, if the displacement is taken as I (x,t).

a a T i=p where T is the curvature of the grid during some instant of vibration.

If Y=p.(x) e where j is,\ 1, w is angular velocity, and t is for time, the equation is as follows:

Win this case is expressed by the following equation:

The solution of the equation (2) can be obtained by the perturbation theory using the equation (3). The frequency cu in such a case can be approximately given by the following equation: i

sin (n=1, 2, 3

It appears from equation (5) that the influence of nonuniformity of the line density of the grid elements on the vibration frequency thereof is maximum at a place where the amplitude of the movement of the grid elements not subjected to perturbation is at a maximum and that this influence is zero at a place where the amplitude is zero.

When the grid elements resonate with an external force, the fundamental vibration (n=l) matters and u,(X) is given as follows:

Consequently, with the line density being selected small in the vicinity of the vibration frequency of the grid elements 13 is great, while the vibration frequency does not vary so much, even if the line density is increased near x=o or x=I.

Accordingly, it will be understood that it is efiective for increasing the fundamental vibration frequency to form each slit 17 wide at the central portion thereof and narrower at the upper and lower end portions.

With the slits 17 of such shape, the resonant frequency of the grid elements 13- becomes high to substantially decrease electron beam deviation and, in addition, the electron beam transmission factor increases at the central portion of the grid structure to increase the luminance of the reproduced picture at the central portion thereof. The deviation of the electron beam, which is caused by the influence of earth magnetism at the upper and lower areas of the reproduced picture, is negligible with my new and improved grid structure.

According to my experiments with a 12 inch color picture tube, good results could be obtained by the use of the slits 17 formed such as depicted in FIG. 4. In the experiments a sheet of stainless steel which was 0.15 mm. thick was used in which the pitch of the slits 17 was 600 microns, the width of each phosphor strip of the phosphor screen was 210 microns and the phosphor strips were arranged in the direction of the slits 17 in the order of red, green and blue. The width B of the slits 17 was selected at points x, ybased upon the following equation.

B (x, y)=l 22dx 2 where a and B are constants.

Since the grid element assembly 10 can readily be produced by a photoetching process, for example, there is no problem in the manufacture of the grid structure. The grid element assembly can also be produced by arranging metal strips at a predetermined pitch, in which case slits similar to the aforementioned ones are formed between adjacent ones of the metal strips. It should be understood that the shape, material and size of the grid elements, plate and the width of the slits may be suitably changed if desired and that the method of manufacture of the plate and for mounting it on the grid frame are not limited by that disclosed herein.

While there been shown and described a single embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and that it is intended by the appended claims to cover all such changes and modifications as fall within the true'spirit and scope of the invention.

I claim:

l. A color video picture tube, comprising a screen having arrays of different color-emitting phosphors and a beam selecting grid structure adjacent said screen and including a plate which is adapted to be charged so as to attract a beam of electrons, said plate having a plurality of elongated, generally parallel slits therein with each of said slits having a width that varies along its length in accordance with the equation: B=K ax /3y in which B is the width of each slit at orthogonally related distances x and y from the center of the plate measured respectively at right angles to the direction of the slit and parallel to said direction, and K, a and B are constants so that each slit is of maximum width at its middle and tapers in the directions at right angles to the direction of the slit from said center of the plate to the slits farthest from said center. 

1. A coloR video picture tube, comprising a screen having arrays of different color-emitting phosphors and a beam selecting grid structure adjacent said screen and including a plate which is adapted to be charged so as to attract a beam of electrons, said plate having a plurality of elongated, generally parallel slits therein with each of said slits having a width that varies along its length in accordance with the equation: B K- Alpha x2- Beta y2 in which B is the width of each slit at orthogonally related distances x and y from the center of the plate measured respectively at right angles to the direction of the slit and parallel to said direction, and K, Alpha and Beta are constants so that each slit is of maximum width at its middle and tapers therefrom to its opposite ends, and further so that the maximum widths of the slits decrease progressively from slit to slit in the directions at right angles to the direction of the slit from said center of the plate to the slits farthest from said center. 